The Flux Ratio of the [OIII]λλ5007,4959 Doublet with Redshift

Abstract

As a test of the time symmetry of forbidden-line emission processes, we measured the [OIII]λλ4959 and 5007 emission lines of more than 12,000 galaxies from the Sloan Digital Sky Survey DR8 to examine the [OIII]λλ4959,5007 flux ratio as a function of redshift z. Using two different approaches, we fitted each line with a Gaussian curve and rejected any spectrum not conforming to requirements of line symmetry, S/N levels, and continuum fit. We found the variance in the ratio of flux to be between 4.7 and −3.3% for 0<z<0.433 which is consistent with no change. After correcting for systematic effects of noise, we found the mean value of the [OIII]λλ4959,5007 flux ratio to be 2.98 ± 0.01 which is consistent with theory and previous studies using AGN spectra. We also used these data to estimate an upper limit on the time dependence of the fine structure constant α of Δα/α(0)<1.4×10−5 for galaxies within the same redshift range. This corresponds to |α−1dα/dt|<2×10−15 yr−1, which is also in line with previous estimates from SDSS QSO data.